High-shielding light-weight cables including shielding layer of polymer-carbon composite

ABSTRACT

A cable for power transmission or communication has a core unit having at least one conductor and an insulating layer surrounding each conductor. A first shielding layer surrounds the core unit and is formed of a polymer-carbon composite in which carbon-based particles are dispersed in a matrix of thermosetting polymer material, the first shielding layer having an electrical resistance of 10 Ω·m or less. A metal-based second shielding layer surrounds the first shielding layer.

RELATED APPLICATION

This application claims the benefit of priority from Korean PatentApplication No. KR 10-2018-0158305, filed on Dec. 12, 2018, the entiretyof which is incorporated by reference.

TECHNICAL FIELD

The present invention relates to a high shielding lightweight cable,more specifically, a cable of reduced weight and improved shieldingefficiency by using a shielding layer made of a polymer-carbon compositecontaining carbon particles having high electrical conductivity.

BACKGROUND ART

Cables, particularly coaxial cables for transmitting power or electricalsignals for communication include various components for transmissionperformance and protection against environmental influences. Generally,such a cable includes a conductor made of solid or stranded wires, aninsulating layer made of a dielectric material for electricalinsulation, and a shielding layer made of a conductive material forelectromagnetic shielding.

Meanwhile, a cable increases in the size and the length as the scale offacilities using the cable increases. Particularly, transportations witha great bulk and advanced technologies such as lorries, ships, trains,aircraft and spacecraft have at least tens of kilometers to thousands ofkilometers of cable. Therefore, the weight reduction of the cable cangreatly contribute to the reduction of weight of vehicles and the energysaving.

Shielding layers conventionally used has been formed by winding foils orweaving tapes or braiding wires all or most of which are made of metalmaterials of high electrical conductivity, and so, in order to lightenthe cable, there has been a demand for shielding layers of newconfiguration and material to replace the conventional shielding layerof heavy metal materials.

For this purpose, a shielding layer is proposed being made of ametal-polymer foil with a polymer film on which a metal foil or a metalfilm such as copper or aluminum. Although such a shielding layer isadvantageous for reducing the weight of cable, it can only be used in alimited environment where EMI is not high because of low shieldingefficiency.

In addition, a shielding layer is proposed using a copper foil with goodshielding efficiency, or a copper foil and a metal foil (or ametal-polymer foil) together. However, since the shielding efficiency ofthe cable including such a shielding layer increases as the coveragedensity of copper braid increases, there is a problem that the diameterand the number of strands of the copper braid have to be increased forhigh shielding efficiency, and thereby the weight of cable is alsoincreased.

On the other hand, there have been attempts to apply to cables thecarbon nanostructures such as carbon fibers or carbon nanotubes that arenot metals but have excellent electrical conductivity and much lighterweight. However, carbon structures of nanometer or micrometer size haveto be applied to the cable in the form of aggregates, but the electricalconductivity and shielding efficiency of the carbon aggregates are farinferior to copper braid. Further, in order to obtain the shieldingefficiency of the copper braiding level, additional processes such asdoping or plating of metal ions on a carbon fiber is required, and theseadditional processes are very time and cost consuming and therebycommercial applications are largely limited. Moreover, there is adisadvantage that, in order to apply the carbon aggregates to the cableas shielding layers, new machines and processes are required in additionto the existing machines and processes.

DISCLOSURE OF INVENTION Purpose of Invention

Therefore, in order to solve the above problems, the object of thepresent invention is to provide a high shielding lightweight cable usingcarbon materials having excellent electrical conductivity but low massthat allows to reduce the weight of a shielding layer and to achieve ahigh shielding efficiency, and which can be manufactured by the existingmachine without extra costly processes.

Technical Solution

To accomplish the above object, the present invention provides a cablefor power transmission or communication comprising: a core unitcomprising at least one conductor and an insulating layer surroundingeach conductor; a first shielding layer surrounding the core unit andbeing formed of a polymer-carbon composite in which carbon-basedparticles are dispersed in a matrix of a polymer material, the firstshielding layer having an electrical resistance of 10 Ω·m or less; and ametal-based second shielding layer surrounding the first shieldinglayer.

The polymer material may have a number average molecular weight of atleast 1,000 g/mol, preferably at least 10,000 g/mol, and more preferablyat least 1,000,000 g/mol.

Such polymer material may be, for example, epoxy, polyester, vinylester, polyetherimide, polyetherketone ketone, polyphthalamide,polyetherketone, polyetheretherketone, polyimide, phenol formaldehyde,bismaleimide, Polyethylene terephthalate, polycarbonate,acrylonitrile-butadiene styrene copolymer, or other thermosettingmaterials.

In addition, the carbon-based particles may comprise particles havingexcellent electrical conductivity. The carbon-based particles may beselected among particles of graphite, graphene, graphene oxide, carbonnanotube (CNT), carbon fiber, carbon black, and any mixture thereof.More preferably, the carbon-based particles can be in a form of powder.That is, the carbon-based particles may be composed of one type ofcarbon material, or a mixture of two or more carbon materials havingdifferent structures and shapes, or may include carbon materials havingadditional treatment in order to improve the electrical conductivity ora degree of mixing with the polymer material.

The polymer-carbon composite can be formed by mechanically mixing thepolymer material and the carbon-based particles at a temperature higherthan the processing temperature of the polymer material, so thatcarbon-based particles dispersed in a matrix of polymer material can beobtained. Here, the processing temperature of the polymer material meansa temperature to physically modify the shape of polymer by mixing,extruding, etc. without degradation of the polymer. For example, saidtemperature can be of at least 40° C., more preferably to at least 60°C., and even more preferably to at least 70° C. The electricalresistance of the first shielding layer can be measured through a lowresistivity tester well-known in the art, and the electrical resistanceof the first shielding layer formed of the polymer-carbon composite is10 Ω·m or less, preferably 1 Ω·m or less. As such, the polymer-carboncomposite according to the present invention has excellent electricalconductivity that can provide a high shielding efficiency.

In the present invention, the electrical resistance can be measured atambient temperature (20° C.)

In the present invention, the first shielding layer formed of thepolymer-carbon composite can be formed by applying uniformly on the coreunit by a conventional melt extrusion process. That is, the firstshielding layer can be formed by extruding the polymer-carbon compositeon the core unit along the longitudinal direction of the cable. Hence,the first shielding layer is preferably an extruded layer. This is oneof the main advantages provided by the present invention. According tothe present invention, the machines used in the conventional extrusionprocess for forming an insulation film or a cover of a cable can be usedin the process of forming a shielding layer of polymer-carbon compositeas it is, and thus a continuous process can be designed including theformation of the shielding layer of polymer-carbon composite on a cablemanufacturing line.

In case of a multi-core cable having a core unit with a plurality ofconductors, the core unit can further comprise filler that assembles theplurality of conductors and fills space among the conductors for acircular cross-section, and the first shielding layer can be formed bymelt-extruding the polymer-carbon composite on the filler.

In addition, around the filler of the multi-core cable, a bedding layerfor fixing the core-filler structure and shape, or an inner sheath layerfor protecting the cable from external impact or corrosion may befurther arranged, and the first shielding layer can be formed byextruding the polymer-carbon composite on the bedding layer or the innersheath layer.

However, the first shielding layer formed of the polymer-carboncomposite may be extruded to serve as filler that fills the space amongthe cores and maintains the shape of the core unit. In this case,separate filler may be omitted, and the first shielding layer functionsas filler in addition to a shield.

Alternatively, the first shielding layer formed of the polymer-carboncomposite may be extruded around the filler to serve as a bedding layerfor fixing the core-filler structure, and thus the bedding layer may beomitted, or the first shielding layer may function the protection of thecable from external impact or corrosion instead of the inner sheathlayer, so the inner sheath layer may also be omitted if specialconditions are not required for the cable in a specific environment.

That is to say, the first shielding layer formed of the polymer-carboncomposite according to the present invention can serve as filler, abedding layer, or an inner sheath layer in addition to a shield withhigh efficiency, and thus the cable can be lightened by omittingseparate filler, a bedding layer, or a inner sheath layer and the like.

In the polymer-carbon composites, the ratio of the content of thecarbon-based particles to the polymeric material can be determined suchthat the first shielding layer satisfies a predetermined electricalresistivity, or the cable satisfies a predetermined shieldingefficiency.

For example, in order to achieve excellent electrical conductivity ofthe first shielding layer and melt processability for the extrusionprocess, the content of carbon-based particles may be 5 parts by weightor more, preferably 10 parts by weight or more, based on 100 parts byweight of the polymeric material. The content of carbon-based particlesmay be 100 parts by weight or less, preferably 50 parts by weight orless, based on 100 parts by weight of the polymeric material.

Moreover, the thickness of the first shielding layer can also bedetermined so as to satisfy a predetermined electrical resistance or apredetermined shielding efficiency.

For example, in order to achieve excellent shielding efficiency andlight weight of the cable, the first shielding layer may be formed to athickness of 0.1 mm to 5 mm, preferably 0.5 mm to 2 mm. However, thethickness of the first shielding layer may exceed 5 mm when a highershielding efficiency is required even if the weight of the cableincreases.

Furthermore, the polymer-carbon composite may be crosslinked to improvethe mechanical and physical durability, heat resistance, oil resistance,etc. of the first shielding layer. For this purpose, the polymer-carboncomposite may contain a crosslinking agent and/or a crosslinkingco-agent. A suitable cross-linking agent and a cross-linking co-agentcan be selected for the cross-linking conditions and mixed together withthe polymer material and the carbon-based particle by means of anordinary mixer such as an internal mixer or a roll-mill mixer. Then,after the first shielding layer is applied on the core unit through meltextrusion process described above, it may be crosslinked through across-linking process such as heating or irradiating ultraviolet light.

The second shielding layer can be formed by taping a metal foil or ametal-polymer foil, or by braiding a plurality of metal strands orstrand bundles of strands. The type of metal constituting the secondshielding layer is a metal having good electrical conductivity such ascopper or aluminum.

When the second shielding layer is formed of a strip-shaped metal foil,it may be made by a helicoidal or longitudinal taping process. Inaddition, when the second shielding layer is formed of a plurality ofmetal strands, it may be made by a braiding process. In this case, thesurface density of the metal braided shielding layer can be determinedsuch that the cable satisfies a predetermined shielding efficiency.

In a preferred embodiment, one or more third shielding layers formed ofa polymer-carbon composite may be added to the radially inside oroutside of the second shielding layer. This third shielding layer canfurther improve the overall shielding efficiency of the cable withoutincreasing the second shielding layer made of metal material.

Advantageous Effects

The cable according to the present invention provides the advantages toreduce the weight while maintaining high shielding efficiency by using ashielding layer composed of polymer-carbon composite having very lowelectrical resistance or high electrical conductivity relative to theconventional cable with a shielding layer composed of only metalmaterial. Thereby, the cable according to the present invention canreduce the weight of vehicle body and increase the fuel efficiency wheninstalled in ships, vehicles, automobiles, aircraft, etc. for powersupply or communication of electronic devices.

In addition, since the carbon particles of micro size are applied in theform of polymer-carbon composite in the cable according to the presentinvention, those can be manufactured using the existing extruder, andthus it is advantageous that the application can be added easily to themanufacturing line without new machines or processes. Furthermore, thecable according to the present invention can achieve the desiredshielding efficiency and the lightening of the cable depending on theinstallation purpose or environment by adjusting the composition ratioof polymer-carbon composite, the thickness of shielding layer and/or thenumber of shielding layers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a cable according to oneembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in more detail withreference to the accompanying drawing.

FIG. 1 is a cross-sectional view of a cable according to one embodimentof the present invention. As illustrated, a cable 10 according to thepresent invention includes a core unit 100, a first shielding layer 200,a second shielding layer 300, and an outer sheath 400. However, thecomponents of the cable 10 in FIG. 1 are illustrative and not limited,and may further include well known cable configurations such as a leadsheath layer, a semiconductive layer, an insulating layer, and a bindertape, whereas in some cases some of the components may be omitted.

The cable 10 shown in FIG. 1 is a multi-core cable including three coresthrough which electromagnetic wave signal is propagated. That is, thecore unit 100 includes three cores 110, and each of the cores 110includes a conductor 111, a conductor outer layer 112 surrounding theconductor, and an insulating layer 113.

The conductor 111 is made of a metal having high electrical conductivitysuch as copper, aluminum, aluminum alloy, or copper coated aluminum. Theconductor 111 may be a solid conductor which is a single body or astranded conductor which is an assembly of a plurality of thin strands.

The conductor outer layer 112 surrounding the conductor 111 is formed bya tape such as a separating tape, a fire resistive tape, a conductivetape or the like which provides a proper function according to the useand environment of the cable 10 through the helicoidal or longitudinaltaping process. The conductor outer layer 112 may be a semiconductivelayer which is formed on the outer surface of the conductor 111 througha melt extrusion process of a polymer composite containing a conductivecomponent such as carbon black and which functions to uniformlydistribute the electric field of the stranded conductor and to mitigatethe partial discharge and the concentration of local electric stress atthe interface between the conductor and the insulating layer. Theconductor outer layer 112 is optional and may be omitted.

The insulating layer 113 surrounding the conductor outer layer 112 maybe formed by melt extrusion of the dielectric onto the outer surface ofthe conductor outer layer 112. For example, if a fire resistive tape ishelicoidal taped on the conductor 111, the insulating layer 113 may beformed by melt extruding the dielectric along longitudinal direction touniformly wrap the fire resistive tape layer.

The conductor 111, the conductor outer layer 112 and the insulatinglayer 113 constitute one core 110 and the three cores 110 form a coreassembly twisted each other by a constant pitch.

On the outside of the core assembly, filler 120 is disposed to assemblethe cores and to fill the gap for circular cross section. The filler 120can be made of polyester, polypropylene (PP), polyvinyl chloride (PVC),ethylene propylene diene monomer (EPDM), ester yarns, amide yarns,polyester yarns, aramid yarns, etc. The material for the filler 120 maybe selected from a various thermosetting or thermoplastic polymershaving physical and chemical properties such as tensile strength,moisture resistance, and flame resistance depending on the usage or theinstallation environment of the cable 10. A bedding layer 130 isdisposed around the filler 120 to maintain the core-filler structure andshape, and it may be made of PVC, PE, polyolefin, or the like.

As described above, in this embodiment, the core assembly of the threecores 110, the filler 120, and the bedding layer 130 around themconstitute a core unit 100. However, the configuration of the core unitis not limited to this, and may be composed of only a single core, or anassembly of two or four or more cores, and the filler 120 and thebedding layer 130 may be omitted depending on the installationenvironment of the cable.

According to the present invention, a first shielding layer 200 formedof polymer-carbon composite is disposed around the core unit 100, and asecond shielding layer 300 based on metal is disposed around the firstshielding layer 200.

The polymer-carbon composite constituting the first shielding layer 200is formed by mechanically mixing the polymer material and thecarbon-based particles at a temperature higher than a processingtemperature of the polymer material. The polymer material may have anumber average molecular weight of at least 1,000 g/mol, preferably atleast 10,000 g/mol, or more preferably at least 1,000,000 g/mol. Suchpolymer materials may be, for example, epoxy, polyester, vinyl ester,polyetherimide, polyetherketone ketone, polyphthalamide,polyetherketone, polyetheretherketone, polyimide, phenol formaldehyde,bismaleimide, Polyethylene terephthalate, polycarbonate,acrylonitrile-butadiene styrene copolymer, or other thermosettingmaterials.

The carbon-based particles are formed of at least one of powders ofgraphite, graphene, graphene oxide, carbon nanotubes, carbon fibers, andcarbon black. That is, the carbon-based particles may be composed of onetype of carbon material, or a mixture of two or more carbon materialshaving different structures and shapes, or may include carbon materialshaving additional treatment in order to improve the electricconductivity or a degree of mixing with the polymer material.

Particularly, the first shielding layer 200 is formed to have anelectrical resistance of 10 Ω·m or less which can be measured by a lowresistivity tester. The first shielding layer 200 can be formed to havean electrical resistance of 10 Ω·m or less, and more preferably 1 Ω·m orless by being composed of the polymer-carbon composite. Thus, the cableaccording to the present invention can achieve high shielding and lightweight by using the shielding layer formed of polymer-carbon compositethat is capable of reducing weight while providing high shieldingefficiency.

The first shielding layer 200 is formed by extruding the polymer-carboncomposite on the core unit 100 along the longitudinal direction of thecable by a conventional melt extrusion process. That is, thepolymer-carbon composite constituting the first shielding layer of thepresent invention can be disposed on the core unit 100 using the machineused in the conventional cable manufacturing process, and no new extramachine or process is required.

In this embodiment, since the core unit 100 includes the filler 120 andthe bedding layer 130 around the core assembly, the first shieldinglayer 200 is formed by extruding the polymer-carbon composite onto thebedding layer 130. However, since the polymer-carbon composite itselfcan serve as filler that fills the gaps of the core assembly to have acircular cross-section, and also as a bedding layer to maintain thecore-filler structure, in other embodiments, the bedding layer, or bothof the filler and the bedding layer may be omitted, and those can besubstituted by the first shielding layer 200 of polymer-carboncomposite.

Although not shown in the FIGURE, an inner sheath layer for protectingthe cable from external impact or corrosion may be added around the coreunit 100. However, the polymer-carbon composite itself can also serve asthe inner sheath layer, and thus the first shielding layer formed of thepolymer-carbon composite can be configured to substitute the innersheath layer.

That is to say, the first shielding layer 200 formed of polymer-carboncomposite according to the present invention can serve as filler, abedding layer, or an inner sheath layer in addition to a shield withhigh efficiency and low weight, and therefore the filler, the beddinglayer, and/or the inner sheath layer can be omitted so that the cablecan be further lightened.

In order to provide excellent electrical conductivity as described aboveand to secure melt processability in a conventional extrusion process,the polymer-carbon composite material of the first shielding layer 200may have 5 parts by weight or more of the carbon-based particles,preferably 10 parts by weight or more, and 100 parts by weight or less,preferably 50 parts by weight or less relative to 100 parts by weight ofthe polymeric material. Particularly, the ratio of the content of thecarbon-based particles to the polymer material in the polymer-carboncomposite is determined so that the first shielding layer satisfies apredetermined electrical resistance or the cable satisfies apredetermined shielding efficiency.

Moreover, the thickness of the first shielding layer 200 is determinedso as to satisfy a predetermined electrical resistivity or apredetermined shielding efficiency, and it can be 0.1 mm to 5 mm,preferably 0.5 mm to 2 mm for excellent shielding efficiency and lightweight. However, the thickness of the first shielding layer may exceed 5mm when a higher shielding efficiency is required even if the weight ofthe cable increases. The thickness of the first shielding layer isdefined as the shortest distance between the upper layer and the lowerlayer adjacent to the first shielding layer, and thus, in thisembodiment, since the first shielding layer 200 is adjacent to thebedding layer 130 of the core unit and the second shielding layer 300,the thickness of the first shielding layer is the shortest distancebetween the outer surface of the bedding layer 130 and the inner surfaceof the second shielding layer 300. In another embodiment where thebedding layer 130 and the filler 120 of the core unit are omitted, thefirst shielding layer 200 is adjacent with the insulating layer 113 ofthe cores, so the thickness of the first shielding layer would be theshortest distance between the outer surface of the insulating layers 113of the cores and the inner surface of the second shielding layer 300.

The polymer-carbon composite may be crosslinked to improve themechanical and physical durability, the heat resistance, or the oilresistance, etc. of the first shielding layer 200. For this purpose, acrosslinking agent and/or a crosslinking co-agent can be added to thepolymer-carbon composite. The crosslinking agent and the crosslinkingco-agent can be mixed by a normal mixer such as an internal mixer or aroll-mill mixer, and after the polymer-carbon composite is applied onthe core unit through a melt extrusion process, it may be crosslinkedthrough a cross-linking process such as further heating or irradiatingultraviolet light.

The second shielding layer 300 can be formed by taping a metal foil or ametal-polymer foil, or by braiding a plurality of metal strands orbundles of strands. The type of metal constituting the second shieldinglayer 300 is a metal having excellent electrical conductivity such ascopper or aluminum.

When the second shielding layer 300 is formed of a strip-shaped metal,it may be made by a helicoidal or longitudinal taping process. Inaddition, when the second shielding layer 300 is formed of a pluralityof metal strands, it may be made by a braiding process, and the metalstrand (or wire) is copper wire, tin-coated copper wire, aluminum wire,aluminum alloy wire, copper coated aluminum wire, and metal compositewire in which copper, aluminum or nickel is plated on a polymer orcarbon fiber. The surface density of the metal braided shielding layeris determined so that the cable satisfies a predetermined shieldingefficiency.

Around the second shielding layer 300 in this embodiment, an outersheath 400 formed of a material suitable for the usage or installationenvironment of the cable 10 is disposed.

However, in another embodiment not shown, one or more third shieldinglayers formed of the polymer-carbon composite such as a first shieldinglayer may be added around the second shielding layer 300, or between thefirst shielding layer and the inner side of the second shielding layer,as needed. Such a third shielding layer can contribute to improve thetotal shielding efficiency of a cable as required, without increasingthe thickness of the second shielding layer of metal material.

Examples

The following is a compared test result of the shielding efficiency andthe weight of a cable according to the present invention and aconventional cable.

In order for the compared test, the core unit of the cables according tothe present invention and the cable according to the prior art wereprepared in the same way as follows:

Copper stranded assembly for conductors were prepared by winding 47strands of tin-coated copper wire with 0.255±0.005 mm diameter to rightwith a pitch of 99.0 mm according to IEC 60228 (class 2). On the copperstranded assembly, two types of fire resistance tapes with differentwidths were wound to form a conductor outer layer composed of twolayers. In particular, one fire resistance tape of a width of 10 mm anda thickness of 0.130 mm (mica-glass tape, SR854G) was helicoidal tapedonto the copper stranded assembly with an allowable overlapping rate of45±5%, and another fire resistance tape with a width of 15 mm and athickness of 0.130 mm was helicoidal taped onto the first fireresistance tape with an allowable overlapping rate of 45±5%. On the fireresistance tape layer, an insulating layer of the copper strandedassembly taped with the fire resistance tapes was formed by meltextruding an insulation compound (E-80, KUKDONG ELECTRIC WIRE CO., LTD)based on an ethylene-propylene copolymer according to IEC 60092-351(HF-HEPR) to a thickness of 0.900±0.100 mm, and then crosslinked in acatenary continuous vulcanization line (CCV line) under high pressureand high temperature. As such, three cores with the copper strandedassembly wound by the fire resistance tapes and covered by theinsulating layer were prepared, and those were assembled by twisting tothe right at a pitch interval of 171.0 mm. In the gaps among the cores,three binder fillers (13500 denier, Sungwon Industries) prepared bycollecting amide fibers in a binder form were arranged for a width of 55mm, and assembled together with the three cores.

Meanwhile, the polymer-carbon composite for the cable according to thepresent invention was prepared as NBR-CNT composite (K-Nanos-INB141,Kumho Petrochemical) which is a mixture of a nitrile rubber (NBR) as amatrix with 20 parts by weight of CNT based on 100 parts by weight ofNBR. Then, the electrical resistance of said NBR-CNT composite wasmeasured at ambient temperature (20° C.) with a low resistivity tester,and the result was 1 Ω·cm.

In order for cross-linking, the NBR-CNT composite was added by 1 part byweight of bis (t-butylperoxyisopropyl) benzene (Perbutyl P, NOFCorporation) as a hydrogen peroxide cross-linking agent relative to 100parts by weight of the NBR-CNT composite, and mixed by a roll-mill mixerfor 5 minutes at a roll temperature of 80° C. (i.e. processingtemperature).

The NBR-CNT composite with the cross-linking agent was prepared in aform of long ribbon for continuous injection, and extruded on the coreunit of core-filler to a thickness of 1 mm to form a first shieldinglayer. After the extrusion process, it was crosslinked in CCV line underhigh temperature and high pressure.

Around the first shielding layer, a second shielding layer was providedby metal-braiding. In order to prevent damages of the shielding layer ofthe NBR-CNT composite, firstly a PET tape of a thickness of 0.05 mm anda width of 50 mm was helicoidally taped, and the metal-braiding wasapplied on the PET tape layer. For the metal-braiding, a copper braidwas used which was made by twisting 16 sets of copper wires each set ofwhich consists of N strands of tin-coated copper with a diameter of 0.3mm at a braiding angle of 36.17° and a pitch of 55 mm. Here, Examples 1to 4 were prepared with N of 9, 6, 4, or 2. That is, each cable ofExamples 1 to 4 have different surface densities of the copper braidshaving 9, 6, 4, or 2 strands of copper.

The surface density of the copper braid can be obtained from thefollowing formula given in IEC 60092-350:2014:

$\begin{matrix}{{G = {\frac{\pi}{2} \cdot F \cdot 100}}{F = \frac{NPd}{\sin\;\alpha}}} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Where G is the surface density, F is the filling factor, a is thebraiding angle, i.e. the angle between the cable axis and the copperwire, d is the diameter of the copper wire, N is the number of thecopper wires constituting the set of the copper wires (carrier), and Pis the number of picks per mm.

Therefore, the surface densities of the copper braids of Examples 1 to 4were 104% (Example 1, SC104), 69% (Example 2, SC69), 46% (Example 3,SC46) and 23% (Example 4, SC23), respectively.

Additionally, Example 5 was prepared to have the same surface density ofthe copper braids (SC46) as that of Example 3, but to replace thefillers of amide fibers with the NBR-CNT composite. In this Example,three cores were assembled without binder fillers, and the shieldinglayer of NBR-CNT composite was extruded on the cores to fill gaps amongthe cores to have a thickness of 1 mm on top of it.

On the other hand, the cable according to the prior art (comparativeexample; Control) was extruded on a conventional SHF2-type bedding layer(XLPO-5, KUKDONG ELECTRIC WIRE CO., LTD) around the filler of the coreunit, and crosslinked in CCV line under high temperature and highpressure after the extrusion process.

Around the bedding layer, a conventional shielding layer was provided bymetal-braiding. In order to prevent damages of the bedding layer,firstly a PET tape of a thickness of 0.05 mm and a width of 50 mm washelicoidally taped as the above Examples 1-4, and the metal-braiding wasapplied on the PET tape layer. For the metal-braiding, a copper braidwas used which was made by twisting 16 sets of copper wires each set ofwhich consists of 9 strands of tin-coated copper with a diameter of 0.3mm at a braiding angle of 36.17° and a pitch of 55 mm. Therefore, thesurface density of the copper braid of the cable of the comparativeexample was 104% as in Example 1.

For the cables of Examples 1 to 5 and Comparative Example (Control), theshielding efficiencies were measured at frequencies in the range of 300kHz to 1 GHz by measuring the transfer impedance and the screeningattenuation according to IEC 62153-4-3:2013 and IEC 62153-4-4: 2015standards through triaxial method by CoMeT 90 system of Guidant Corp.The weights of the cables were determined by preparing 5 m of eachcables and averaging the weight of five samples each cut in 1 m.

The result of measurements of the shielding efficiencies and weights ofthe cables of Examples 1 to 5 as well as Comparative Example were shownin the following table:

TABLE 1 Shielding Efficiency (dB) Weight (g/m) 300 3 30 300 1 ReductionCable kHz MHz MHz MHz GHz ratio (%) Comparative 85 66 53 44 55 300Example (Control) Example 1 (SC104) 85 67 55 56 57  280 (6.7%) Example 2(SC69) 76 58 45 47 54 255 (15%) Example 3 (SC46) 71 52 38 41 52 235(22%) Example 4 (SC23) 68 48 33 37 47 220 (27%) Example 5 (SC46) 82 5744 46 58 225 (15%)

As can be seen from Table 1, when a nonconductive SHF2 bedding layer ofthe conventional cable (Comparative Example) with the same surfacedensity of 104% of the copper braided shielding layer was replaced bythe NBR-CNT composite shielding layer (Example 1), the shieldingefficiency was improved in all the frequency ranges. In particular, itis note that the shielding efficiency of Example 1 was improved by about27% compared to the Comparative Example at 300 MHz. This means that thecable of Example 1 (SC104) including the NBR-CNT composite shieldinglayer according to the present invention has high shielding performancethat can be used in an environment of severe electromagneticinterference (EMI). Moreover, the cable of Example 1 (SC104) accordingto the present invention showed a weight reduction of about 6.7% perunit meter compared to the Comparative Example. This is because thespecific gravity of the NBR-CNT composite used in the cable according tothe present invention is 1.12 which is lower than the specific gravityof 1.20 of the SHF2 bedding layer of the conventional cable.

In addition, considering that the shielding efficiency required forgeneral signal/control cables is 40 dB or more, the cable of Example 2(SC69) with the reduced surface density of the copper braid shieldinglayer by 69% as well as the NBR-CNT composite shielding layer accordingto the present invention showed a shielding efficiency of more than 40dB in all of the measured frequency ranges, and thus can be usedsufficiently as a lightweight cable.

The cables of Example 3 (SC46) and Example 4 (SC23) according to thepresent invention were reduced in weights by 22% and 27% respectively byusing the NBR-CNT composite shielding layer as well as the copperbraided shielding layer with greatly reduced surface densities by 46%and 23%. Although the cables showed the shielding efficiencies less than40 dB in some frequency ranges, those could be used in other frequencyranges where the shielding efficiency is more than 40 dB, or in anenvironment where electromagnetic interference is not severe as alightweight cable.

Furthermore, even if the surface density of the copper braid shieldinglayer is significantly reduced as in the cables of Examples 3 and 4,Example 5 shows the shielding efficiency more than 40 dB in all thefrequency ranges by making the NBR-CNT composite shielding layer thickerand omitting the filler in the core unit. In addition, it would also bepossible to pull up the shielding efficiency to more than 40 dB byincreasing the content of CNT particles in the NBR-CNT composite, or byfurther adding a NBR-CNT composite shielding layer on the copper braidedshielding layer.

While the present invention has been described with reference to thelimited embodiments and FIGURES, it is not to be restricted by theembodiments, and those skilled in the art may implement various changesor modifications from the description. The spirits of the presentinvention should be grasped only by the claims described below, and allthe equal or equivalent modifications of the claims are intended to fallwithin the scopes of the invention.

DESCRIPTION OF REFERENCES  10: Cable 100: Core unit 110: Core 111:Conductor 112: Conductor outer layer 113: Insulating layer 120: Filler130: Bedding layer 200: First shielding layer 300: Second shieldinglayer 400: Outer sheath

The invention claimed is:
 1. A cable for power transmission orcommunication comprising: a core unit having at least one conductor andan insulating layer surrounding each conductor; a first shielding layersurrounding the core unit and being formed of a polymer-carbon compositein which carbon-based particles are dispersed in a matrix ofthermosetting polymer material, the first shielding layer having anelectrical resistance of 10 Ω·m or less, and wherein the first shieldinglayer has a thickness of 0.1-5 mm; and a metal-based second shieldinglayer surrounding the first shielding layer.
 2. The cable according toclaim 1, wherein the thermosetting polymer material has a number averagemolecular weight of at least 1,000 g/mol.
 3. The cable according toclaim 1, wherein the carbon-based particles comprise at least particlesselected among particles of graphite, graphene, graphene oxide, carbonnanotubes, carbon fibers, carbon black, and any mixture thereof.
 4. Thecable according to claim 1, wherein the polymer-carbon composite isformed by mechanically mixing the thermosetting polymer material and thecarbon-based particles at a temperature higher than a processingtemperature of the polymer material.
 5. The cable according to claim 4,wherein the ratio of the content of the carbon-based particles to thethermosetting polymeric material in the polymer-carbon composite, or thethickness of the first shielding layer is determined such that the firstshielding layer satisfies a predetermined electrical resistivity, or thecable satisfies a predetermined shielding efficiency.
 6. The cableaccording to claim 4, wherein the content of the carbon-based particlesare 5 parts by weight or more and 100 parts by weight or less based on100 parts by weight of the thermosetting polymeric material.
 7. Thecable according to claim 1, wherein the first shielding layer is formedby melt extrusion of the polymer-carbon composite along the longitudinaldirection of the cable on the core unit.
 8. The cable according to claim7, wherein the core unit includes a plurality of conductors, and fillerthat assembles the plurality of conductors and fills space among theconductors for a circular cross-section, wherein the first shieldinglayer is formed by melt-extruding the polymer-carbon composite on thefiller.
 9. The cable according to claim 7, wherein the polymer-carboncomposite of the first shielding layer serves as filler, a bedding layeror an inner sheath layer around the core unit.
 10. The cable accordingto claim 1, the polymer-carbon composite can be crosslinked with across-linking agent and/or a crosslinking co-agent.
 11. The cableaccording to claim 1, wherein the second shielding layer is formed bytaping a metal foil or a metal-polymer foil or braiding a plurality ofstrands of metal strands.
 12. The cable according to claim 11, whereinthe second shielding layer is formed by braiding a plurality of metalstrands, wherein the surface density of the metal braid is determinedsuch that the cable satisfies a predetermined shielding efficiency. 13.The cable according to claim 1, further comprising at least one thirdshielding layer formed of the polymer-carbon composite inside or outsideof the second shielding layer in the radial direction.
 14. A cable forpower transmission or communication comprising: a core unit having atleast one conductor and an insulating layer surrounding each conductor;a first shielding layer surrounding the core unit and being formed of apolymer-carbon composite in which carbon-based particles are dispersedin a matrix of thermosetting polymer material, the first shielding layerhaving an electrical resistance of 10 Ω·m or less, and wherein the firstshielding layer has a thickness equal to or less than 2 mm; and ametal-based second shielding layer surrounding the first shieldinglayer.